Wireless communications enable a wide variety of applications, such as satellite transmission, radio and television broadcasting, sensor networks, global positioning system (GPS), and mobile communications. Emerging technologies have led to a new generation of multifunctional, small-size, and low-cost communications devices that cover a wide variety of wireless communications applications.
As the demand for multifunctional wireless communications devices increases, so does the demand for smaller, low-cost, and single-chip oscillators, mixers, and radio frequency (RF) front-end and intermediate frequency (IF) filters that can bring together in a single device multiple wireless standards operating at different frequencies, without compromising size, portability, and cost. Currently, the majority of the modern transceiver systems are based on heterodyne architectures, which utilize a number of discrete resonant components such as quartz crystals, surface acoustic wave (SAW) devices, and thin film bulk acoustic resonator (FBAR) devices to implement oscillators with high quality factors (Qs) for frequency reference and band-pass filtering.
Despite the beneficial high Qs offered by quartz crystal and SAW devices, and the low motional resistance provided by FBARs, they are relatively bulky off-chip components that must be integrated with electronics at the board level, thus hindering the ultimate miniaturization and portability of wireless transceivers. It can therefore be appreciated that it would be desirable to have on-chip devices that provide the same functionality.